Aum Acoustics

EF86 Guitar Amplifier

NOS Tesla/Telefunken EF86, NOS Philips Miniwatt 12AX7, Winged C KT88, NOS Mullard GZ34


This is a new guitar amplifier that I just completed. It’s designed to provide a really beautiful “clean” tone for a hollow body arch top guitar or a semi-hollow guitar as an alternative. It’s voiced for an excellen jazz tone and will not include a master/volume knob to send the amp into distortion. It is an excellent platform for attaching guitar pedals, and can use a distortion pedal to obtain excellent tonal shifts if you desire.

My favorite distortion pedal is the Gregor Hilden Signature Okko FX GH Diablo effects pedal. With that connected to the front end of this amplifier, you have access to one of the most beautiful distortion tones possible (in my opinion). Try it and you’ll end up really liking this solution. Of course you can use other really excellent distortion pedals like those made by Kingsley and others.

I’ve removed all of the tone sucking features that plague most guitar amps. There isn’t reverb or a send/return effects loop or a master/gain pair of pots. However, the tone control circuit that includes bass, mid and treble really is a necessity and I do include that. Normally, adding a tone circuit reduces volume and to prevent that from happening, I’m using a 12AX7 tube to replace the gain lost by inclusion of this circuit. I’ve owned several SuperBaby amplifiers and found that removing the tone circuit made the amp sounds its best. However, I really need tone control to “sculpt” the ideal tone for my guitars and the 12AX7 gain that’s added is a perfect compliment. Also, the SuperBaby doesn’t use a proper single ended output transformer and its push pull OT is really inadequate and will eventually lead to many problems. The 15W single ended 8 ohm output transformer that I use (and of course the really large power transformer) is ideal for this circuit and it allows the use of many large output tubes with the KT88 and EL34PH my favorites.

The EF86 is the first stage input tube and in my opinion, does a better job of providing a beautiful clean tone than when using a typical 12AX7 first stage tube. It is potentially very microphonic, however, and to prevent problems, I use a much lower operating voltage on that tube than is typical. That really helps and then I also suspend it on a tube socket plate that is mounted underneath the chassis and isolated from the top plate by sorbane washers. Then I add a Herbies titanium vibration damping ring and only use NOS EF86 tubes that sound good and don’t have the typical microphonic issues. Yes, this is a lot of work but endowing this first stage with the EF86 tube is worth it and is what makes this amplifier really special. The few commercial alternatives that you’ll find that use the EF86 tube typically place that tube in the 2nd tube stage with the 12AX7 as the first stage input tube. Here, I’m using the EF86 in the first stage and I absolutely love it. I highly recommend the NOS Tesla produced EF86 for this 1st stage preamp tube.

Even in the 2nd stage, the 12AX7 that is used for the tone controls still must be really good. It effects the tonality of this amp and the nicest sound quality I’ve found is when using the NOS Phillips Miniwatt 12AX7. Other new production 12AX7 tubes don’t sound good at all (very flat, uninteresting, and too scratchy) and really detract from the potential sound quality this amp is able to generate. If you’re looking for an alternative, the NOS Mullard 12AX7 is a possibility as well as a NOS RCA clear top 12AX7. I wouldn’t recommend less than what these 3 beautiful NOS tubes offer. The sweet sound these 12AX7 tubes create in the 2nd stage is necessary to provide the “icing” on the cake so to speak of the other tubes. Do not compromise with this tube selection.

 I’ve used my Sadowsky SS-15 to fine tune this amp and it now sounds beautiful. My favorite 2 power tubes for this amplifier are the KT88 and EL34PH. I’ve set the cathode resistor and other circuit voltages to optimize those two tubes. I’ve also tied pins 1 and 8 together to be able to properly play the EL34 tube while not affecting the KT88. This is critical to be able to use the EL34 as one of the power tube selections.

 The EL34PH that I use provides a “romantic” sound quality yet isn’t too thick or muddy as is typical of this tube in many amps. The KT88, however, provides the best clean tone I’ve come across so far and is my favorite tube for this amp:

NOS Tesla/Telefunken EF86, NOS Philips Miniwatt 12AX7, Pavane EL34PH, NOS Mullard GZ34

The KT88  provides the most linear tube sound quality while allowing all 6 strings on my guitar to sound good at all fret positions.The EL34 is a bit “fuzzy”and “soft” when using the 3 lower frequency strings. The KT88 is better for playing on all frets but it’s really nice to be able to change tone by just swapping out one tube. Use the EL34PH when you start getting bored and you have a whole new tone and a different guitar amp. This prevents monotony when playing the amp for many hours and is just plain fun.

This amps sound quality is better than a solid state amp (even though I really like the sound quality provided by my Quilter ToneBlock 202) since the 2nd order harmonics from the tubes creates a beautiful 3 dimensionality and wider sound stage. Without tubes, things are a bit mental sounding and as a result, my Quilter doesn’t really have the soul of a tube. I play the Quilter for awhile and really like it. But after maybe 5 minutes of playing, I don’t have the emotional attachment to my sound that I get when using this EF86 tube amp and I then change my mind and head for the tube amp. That’s where I gain the greatest enjoyment – playing the EF86 tube amp!

I run the voltages in this amp at a lower level (on both the power and preamp tubes) to keep the signal as clean as is possible and to keep both tubes in their most linear range. I’ll post voltage levels at all test points when I have time so you’ll be able to see exactly where I’ve set the limits for this amp.This approach provides a really beautiful clean tonal quality (full of really good tone). The EL34 tube I’ve chosen sounds excellent and is one that is easy to obtain so you don’t need to worry about finding progressively harder to find and expensive matched tubes. The KT88 also is easy to source and I like the Winged C KT88 the best even though I used an expensive and rare Genalex KT88 (as well as many other KT88 tubes) when going through my testing of this amp. The Genalex makes no sense financially and I actually like the presentation of the Winged C even better. So forget spending $400 or more on this rare single power tube. It doesn’t make any sense.

I’m using all really high quality parts that are extremely unusual to include in a guitar amp so this is not a cheap build placed in a “tin can” type of chassis with a heat imposing enclosure. Plus, all tubes are upright (as they should be) and the chassis is not enclosed to allow for really excellent heat dissipation. I just can’t understand why someone would hang a guitar amp upside down (with tubes pointing down) and have all of the heat raising upward while frying and baking the components above it. I also don’t understand why an amp would be placed in an enclosure that can’t breath well like most heads or combo amps. Heat is the main enemy of your expensive amps and tubes. Really excellent ventilation is your savior. So creating a really excellent cnc”d 1/8″ thick aluminum chassis that looks good and allows the best ventilation makes the most sense. It also is a great design approach and it allows me to make the chassis bigger than normal guitar amps so components can be spread out properly and heat as well as electrical interference can be minimized.

Why vastly limit the life of your components and basically “fry” their insides. NOS tubes are rare and expensive and care should be used to optimize their life span. These are issues that have always bothered me and why I’ve built audio components for listening instead of guitar amps used to create music. However, if you agree with my concerns, I’m finally providing you with a proper way to use a well designed guitar amp. My approach is very different and I’m sure you can relate to it. I use only 1 superb power tube and also use a 100db sensitive guitar speaker to obtain beautiful 8-9 watts of clean power. This is plenty loud for most any use (practice or recording) in a small to medium sized room.

This amp marks the beginning of my work with guitar amps instead of building and selling  just really high-end audiophile oriented equipment. I’m also going back to my roots in music (as a creator and not just a listener) and am now working with recording studio gear and will be representing and selling just a few really stellar component solutions – ones that I use myself and really like.

I’m more interested in helping others create beautiful sounding music than I am in helping them to listen to music passively. Too many audiophiles don’t know what really good recorded music sounds like and they tilt their audio systems to sound like what they desire. However, the actual recorded tracks were never meant to sound like that. Going back to my professional piano playing days and to when I built several recording studios is what I’m now doing and is the reason for changing to guitar amps and recording gear.

The only audio listening only component that I will continue to build will be my unique super high end tube buffer. I’ve worked on that one so hard its difficult to imagine anything better anywhere near its price range. Parts cost alone is $3,000 and its built at a much higher quality level than most other gear. The goal of that component is to provide the absolute cleanest 2nd order harmonics possible without degrading the audio signal that we originally recorded. I accomplished that and is the reason this single tube “buffer” will remain a permanent OEM product. However, when recording, the Dangerous Music gear works much better and is my recommendation on the creation side of things.

You will notice that I use a really high quality cystom 1/8″ aluminum cnc’d chassis (in both the tube buffer and the guitar amplifier) and that it is extremely solid and robust. Not many guitar amps are built this well

 However, I don’t go overboard on embellishing the chassis to waste money. The chassis is created this way to provide proper design, longevity, and excellent vibration control. In my opinion (and through much hands on experience) the circuit design utilized is the most important element to include first. Then parts selection becomes important – but only if the circuit design is way above average. Bling isn’t necessary beyond making something ergonomic to use and really good to look at. I’m really good at making my designs look beautiful even though I could make even more money if I was interested in adding more “bling” and marketing my creations through typical sales channels.

I’d rather build for longevity than waste money needlessly on exotic and unnecessary chassis design even though I do love beautiful design. You can see that in my work as I try to make anything that I create beautiful. My OEM components already have enough money in just their parts cost to justify their existence and higher price tag. Adding labor and other required costs (to stay in business) makes the resulting price level really high and high enough. I don’t use a dealer/distributor network that triples that cost and I price what I make just to get by. So anything that you purchase from me will provide a superb value or I won’t offer it. It’s as simple as that. The Pro Audio gear that I also represent has such low margins that I really don’t make a lot of money selling it. However, it is necessary as part of the ideal solution that I keep reaching for and achieving.

Let me know if you have any questions. This guitar amplifier will be available by the end of 2020 and be a custom build (available by preorder) anytime thereafter. I will make only one of these amps available for sale at parts cost without any markups for my time or profit. The construction time frame on all custom order amps will be around 10 weeks and will require full payment for parts cost up front. The remaining amount will be due prior to shipping and will be for my time involved plus the actual shipping cost.

The chassis cnc metal and anodizing work and transformer construction takes the longest time with a 6-8 week approximate delivery time (from them to me) as a minimum. While waiting, however, I do build out the amp as far as I can (as you see in the photos shown below) so the final build doesn’t take as long and I can test and ship the amp in a reasonable time period thereafter.

I’ll update this page when this amp is ready for new orders

I Built A 2nd Top Plate To Fit Larger Rectifier & Power Tubes Base Diameters
This Photo Shows The 2 Big Tube Hanging Plates For The Tube Sockets

The Ideal Speaker & Cabinet For This Amp?

Here’s a photo of the new speaker cabinet that was created just for this amplifier:

The Ideal Speaker Being Mounted In This Cabinet?
The Very Musical 12″ Celestion Creamback 75, 8ohm


Repair Information

If you have any problems connecting this guitar amplifier to your current system, please let me know. If you perform any repairs yourself, you void any kind of warranty or repair policy that I might have. Also, if you purchase a component from me at parts cost without any markup for profit or my time, you also are on your own since there is no margin for my spending time or investing additional parts cost to repair something.

However, I will be glad to help you on the phone regarding possible problems that you might have with any of your audio components and I’ll be glad to share the circuit design layout, schematic, and parts list for this piece of equipment – always! This will allow you to easily repair (or get repaired locally) something that might have been “fried” from improper connections or other issues. This component is built to last a very long time and was one of my goals for its design. It is archival in build quality and should provide many dedcades of pleasurable use. All parts used are of the highest possible quality.

Ground loops are the typical issues that someone will have when connecting complimentary components that are designed “outside of the normal electrical specifications”. Some manufacturers do this to get their equipment to sound good. However, then you are pretty much captive to using their components. In my opinion, that’s not a good way to create a superb audio system. Make sure all of your components are built according to normal standards and work well with all other equipment (if of course, those components are designed properly).

I will be glad to discuss equipment compatibility with you prior to your purchasing anything that I build or sell